Anyone with a heat pump water heater

Most HPWHs are "hybrid water heaters", with both a heat pump and a conventional element.

Like any heat pump, they are better at extracting heat from the surroundings when the surroundings are warmer. So they'll be a nice win during warmer months when they can easily extract heat from the unconditioned or semi-conditioned surroundings, and during those months you are probably not trying to heat those surroundings.

In cooler months, things are more equivocal. The surroundings are probably cooler, so it won't be extracting as much heat from them as before (or it would have to run longer to do so), and depending on how unconditioned the space is or isn't, your central heat might be putting some of that heat back. Depending on how the HPWH's 'hybrid' parameters are set, it might just decide to use its conventional heat element instead.

The units I've seen have available duct kit accessories: you can decide where you want the warm air to come from, and where you want the cooler, dehumidified air to go. You could even, maybe, make seasonal choices, with a three-way damper in your duct. In summer, I might want one to just recirculate basement air and dehumidify it. In winter, maybe I could think about ducting from the attic, where there might be some heat available from the sun baking the roof. I don't know if anybody really bothers with that though.

Even if it is just helping itself to heat from the central heating, that still may not be so terrible, depending on how efficient that system is. If that's also a heat pump, or coming from solar, etc., so much the better.

I don't have a heat pump heating the house yet. In my situation, i think that's the lower-hanging fruit, before I think about changing the WH.

 

While it is taking heat from the space, it is also dehumidifying it. Which could be helpful, depending.

Might also be possible to duct them to put the cold exhaust where you want it.

 

My older heat pump water heater (HPWH) is in an unsealed, unconditioned garage, nearly ideal for my climate. It optionally could take an exhaust vent, which I did make use of, with a diverter valve to somewhat cool the garage in summer. Very many newer models can accommodate both intake and exhaust venting. Putting it in a heated / conditioned space without such venting violates local rebate requirements in this heating-dominated climate zone. With venting, it can go where ever you want.

I believe our local rebates allow unvented units in sealed spaces that are unconditioned and exceed a certain volume. While this is less efficient than venting or unsealed spaces, there is a presumption that enough heat flows in through the walls of such large-enough spaces to allow the unit to operate with acceptable efficiency, still far better than traditional resistance heaters.

In an AC-dominated climate, it could make sense to keep the HPWH inside the conditioned space. This lets the electric energy do double-duty, both heating the water and cooling the house interior. Your utility should have a decent idea whether this approach is reasonable for typical homes in its service areas. Combined heat pumps that are designed to do both, can have some extraordinarily high "efficiency" figures.

For my house, an upgrade from traditional electric to a ductless minisplit heat pump for space heat, is the largest fruit on my conservation tree. The heat pump water heater is the second largest. Various insulation upgrades, air infiltration sealing, improved solar heat gain management, appliance efficiency upgrades, and glass upgrade (patio slider only), where smaller fruits. Though I did not compute the "fruit size" vs cost of any of them.

Fruits of my solar PV system are assigned to the production tree, not the conservation tree.